For example, as described in Japanese Patent Application Laid-Open No. 2006-192467, a servo-press machine has a feature that an operation of a slide can be variably controlled in response to various requests so that an operation pattern of the servo-press machine can be selected.
In the servo-press machine, a torque capacity of the servo-press machine (capacity expressed by the amount of pressure which can be generated and a distance in millimeter above bottom dead center (BDC) where the pressure is generated) and a press operating speed (strokes per minute (SPM)) which can be achieved at the time when the pressure is generated depend on the capacity of a servomotor which is used for the servo-press machine.
Specifically, the characteristics of the press machine such as the torque capacity and the production speed are determined by a maximum rotation speed and a maximum torque characteristic of the motor. Therefore, if the torque capacity and the production speed obtained only with the used motor are insufficient, a method involving performing pressurization by using a plurality of motors, that is, the combination of the servomotor and a linear motor (see Japanese Patent Application Laid-Open No. 2001-150193, and the like) and a method involving switchably using a plurality of motors for different steps performed by the press machine (see Japanese Patent Application Laid-Open No. 2008-119737, and the like) have been proposed.
Although an object of a press process including press working can be achieved with the methods described in Japanese Patent Application Laid-Open No. 2001-150193 and Japanese Patent Application Laid-Open No. 2008-119737, there is a fear in that the press machine becomes complex due to the use of the plurality of motors or the use of the plurality of motors separately for the different steps.